Fabrication Of Two-dimensional ReS₂ Based Van Der Waals Heterojunctions And Investigation Of Their Optoelectronic Properties

Due to the fact that there are no dangling bonds on the surface of two-dimensional（2D）layered materials and the unique interlayer interaction,a variety of 2D materials with different properties can be stacked vertically to form a new heterostructure.This new structure constructed by the interlayer van der Waals forces is called van der Waals heterojunctions.This structure can not only integrate the advantages of a single material,but also show the new characteristics that a single material does not have,so as to achieve the"1+1>2"effect,which promotes the application of 2D materials in multi-functional devices..Compared with traditional transition metal dichalcogenides（Mo S₂,WS₂,etc.）,Re S₂has many unique physical and chemical properties,such as weak coupling between layers,anisotropy and so on.At present,a large number of researches have been carried out on the electrical,photoelectric and linear optical properties of Re S₂,but the research on Re S₂based van der Waals heterostructures and their optoelectronic properties is relatively few,and many new properties need to be explored.In this work,two kinds of Re S₂based van der Waals heterostructures were fabricated by mechanical exfoliation and dry transfer,and Au electrodes were prepared by deionized water assisted transfer method.Then the electronic and optoelectronic properties of the device was studied.The main results are as follows:（1）Although the photodetectors based on Re S₂have very high responsivity and polarization sensitivity,their light response speed is usually slow.In order to solve this problem,we designed and prepared Re S₂/WS₂van der Waals heterojunction.Due to the difference of Fermi levels,the Re S₂/WS₂heterostructure exhibits a good photovoltaic effect.An open circuit voltage of about 0.2 V is obtained under405 nm laser irradiation,which makes the device self-driving.Under zero bias,the current switching ratio of Re S₂/WS₂van der Waals heterojunction is more than 10~3,and the responsivity,specific detectivity and response speed are 58 A W^-1,2.8×10¹⁰Jones,and 1.6 ms,respectively,and this speed is much faster than that of Re S₂and WS₂photodetectors.In addition,because the gate voltage can regulate the Fermi level of WS₂and Re S₂,the rectification direction of the device is reversed under the control of the gate voltage.These results have certain reference value for the application of 2D materials in the field of optoelectronic devices.（2）In order to obtain the photodetectors with broad spectral response,low dark current and high responsivity,we have fabricated visible and near infrared photodetectors based on Re S₂/Ge Se van der Waals heterojunction.Compared with the Ge Se photoconductive photodetector,the built-in electric field formed between n-type Re S₂and p-type Ge Se successfully suppresses the dark current of the device and improves the responsivity(2.1×10~3A W^-1).We analyzed and discussed the optoelectronic response characteristics of the device in visible and near-infrared（808 nm）region.Under 1 V bias,the device shows high optical switching ratio and fast response time in visible light rang.In addition,the rectifying direction of the Re S₂/Ge Se heterostructure can be controlled by adjusting the gate voltage.These results indicate that the Re S₂/Ge Se heterostructure has a great prospect in the application of photodetectors with broad spectral response at room temperature.